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March 16, 2009
Novel pandemic flu vaccine effective against H5N1 in mice

By Quinn Eastman

Vaccines against H5N1 influenza will be critical in countering a possible future pandemic. Yet public health experts agree that the current method of growing seasonal influenza vaccines in chicken eggs is slow and inefficient.

Scientists at the Emory Vaccine Center have developed an alternative: virus-like particles, empty shells that look like viruses but don’t replicate. Mice immunized by nose drops with the virus-like particles (VLPs) were protected for months against an otherwise lethal H5N1 infection.

The results are described in the February issue of PLoS (Public Library of Science) ONE.

In mice, VLPs appear to deliver several times more potency per microgram than other types of vaccines, such as the chemically inactivated subunit viral vaccine currently used in the United States or a single viral protein produced in baculovirus.

“This extra potency is important because these other types of vaccines require relatively high doses to be effective for most people, and in a pandemic demand might run up against production capacity. VLPs could offer more bang for the buck,” microbiologist Richard Compans says.

Several worldwide influenza outbreaks have occurred during the past century, with the worst being the Spanish Flu of 1918, which killed more than 50 million people.

The H5N1 variant of influenza, found among birds in Asia in the 1990s, has killed the majority of the several hundred people known to have been infected with it. Public health officials fear that H5N1, to which the human population has not developed immunity, could evolve to be transmissible between humans and cause a global pandemic with very high mortality.

Making influenza vaccines in chicken eggs poses several disadvantages. Producing vaccines takes months. Making enough for millions of people could severely stress the world’s vaccine-making capacity, especially since the poultry industry would probably be crippled in a pandemic. In addition, work with live H5N1 virus is dangerous and should only be performed in special laboratories.

VLPs are made by introducing three separate viral genes into baculoviruses, which only infect insect cells.